This invention relates to a process for the preparation of phenylene diacetate. More particularly the invention relates to the conversion of phenyl acetate to phenylene diacetate by a palladium catalyst in the presence of oxygen, acetic anhydride and acetic acid at elevated temperatures and pressures. Still more particularly the invention relates to a method of preparing para-phenylene diacetate as a major product. Phenylene diacetate may have utility as a solvent. Preparation of phenyl acetate is disclosed in U.S. Pat. No. 4,156,783.
The acetoxylation of chlorobenzene by Pd(OAc).sub.2 in acetic acid with an oxygen atmosphere and with and without the presence of NO.sub.2 and with meta-selectivity is reported in Acta Chemica Scandinavica B28 (1974) 771-776, L. Eberson, et al. "Ac" as used herein refers to the acetyl group, ##STR1## and "OAc" means the acetoxy group, ##STR2## The latter reference also discloses the stoichiometric acetoxylation of phenyl acetate by 2,2'-Bipy Pd(OAc) (NO.sub.3) in acetic acid at 115.degree. C. in an oxygen atmosphere with meta-diacetoxybenzene (meta-phenylene diacetate) being the major product (60%) after a reaction period of 2 hours. The aforementioned reference, pages 597-602, states that a heterogenous gas phase acetoxylation of a monofunctional benzene derivative that takes place in acetic acid in the presence of oxygen shows a reversal of the normal substituent effect, i.e., ortho-, para-directing substituents give predominantly meta-acetoxylation and meta-directing ones give ortho-, para-acetoxylation.
Formation of methylbenzylacetate via the homogeneous reaction between palladium(II) acetate and para-xylene in acetic acid in the presence of oxygen has been studied and reported in articles in Acta Chemica Scandinavica 27, 1973, L. Eberson et al., pages 1162-1174, 1249-1254, 1255-1267. The acetoxylation of phenyl acetate by potassium peroxydisulfate with Pd(II) as a catalyst in the presence of acetic acid to form 25% ortho-, 42% meta- and 33% para-isomers of phenylene diacetate is disclosed in Acta Chemica Scandinavica B30 (1976) pages 361-364, Eberson et al.
The use of palladium(II) (along with other components such as oxidants, cooxidants) to catalyze aromatic acetoxylation is reported in the literature as exemplified by U.S. Pat. No. 3,772,383; Tetrahedron Letters No. 58, pp. 6123-6126, 1968, C. H. Bushweller; J. Org. Chem., Vol. 36, No. 14, 1971, P. M. Henry; and J.S.C. Chem. Comm. 1974, pages 885-886, L. Eberson et al.
The acetoxylation of benzene to phenyl acetate using oxygen, palladium on silica or alumina in the presence of acetic acid is reported in Erdol Und Kohle, 23, 79, 1970.
According to Journal of Organic Chemistry, Vol. 33, Nov. 11, 1968, D. R. Bryant et al., acetoxylation of toluene in the presence of oxygen palladium acetate and an alkali metal carboxylate at elevated temperatures results in a benzyl acetate and at higher conversions, benzylidene diacetate.
However, none of the previously mentioned references disclose or suggest the conversion of phenyl acetate to phenylene diacetate via applicants' method. Further, contrary to the previously discussed reference (Acta Chemica Scandinavica B-28, pages 597-602 and pages (771-776), applicants' method yields predominantly the para-phenylene diacetate isomer.